In order to clarify the association between HBV mutations appearing before and during interferon therapy and the therapeutic effects, serial serum samples from 100 HBeAg-positive CHB patients undergoing peginterferon alfa-2a therapy will be collected and analyzed for the mutations of preS/S gene and BCP-preC/C region, particularly for the deletion mutations. Furthermore, Real-Time PCR will be performed to measure the ratios of wild-type HBV and deletion mutant HBV before and at the end of peginterferon alfa-2a therapy. Finally, statistical analysis will be done to elucidate whether the mutations of preS/S gene and BCP-preC/C region have any relation with the therapeutic effect of peginterferon alfa-2a.